1. Technical Field of the Invention
The present invention relates generally to wireless communication systems and, more particularly, to a frequency planning scheme for use with the operation of a local oscillator in a wireless communication device.
2. Description of Related Art
Mobile communication has changed the way people communicate and mobile phones have been transformed from a luxury item to an essential part of every day life. The use of mobile phones today is generally dictated by social situations, rather than being hampered by location or technology. While voice connections fulfill the basic need to communicate, and mobile voice connections continue to filter even further into the fabric of every day life, the mobile Internet and moving video, including broadcast video, are the next steps in the mobile communication revolution. The mobile Internet is poised to become a common source of everyday information, and easy, versatile mobile access to this data will be taken for granted. Similarly, video transmissions to handheld user equipment will allow movies and television programs to be viewed on the go.
Third generation (3G) cellular networks have been specifically designed to fulfill many, if not all, of these future demands. As these services grow in popularity and usage, factors such as cost efficient optimization of network capacity and quality of service (QoS) will become even more essential to cellular operators than it is today. These factors may be achieved with careful network planning and operation, improvements in transmission methods, and advances in receiver techniques. To this end, carriers want technologies that will allow them to increase downlink throughput and, in turn, offer advanced QoS capabilities and speeds that rival those delivered by cable modem and/or DSL service providers. In this regard, networks based on Code Division Multiple Access (CDMA) technology or Wideband Code Division Multiple Access (WCDMA) technology may make the delivery of data to end users a more feasible option for today's wireless carriers.
The General Packet Radio Service (GPRS) and Enhanced Data rates for GSM (EDGE) technologies may be utilized for enhancing the data throughput of present second generation (2G) systems such as GSM. The Global System for Mobile telecommunications (GSM) technology may support data rates of up to 14.4 kilobits per second (Kbps), while the GPRS technology may support data rates of up to 115 Kbps by allowing up to 8 data time slots per time division multiple access (TDMA) frame. The GSM technology, by contrast, may allow one data time slot per TDMA frame. The EDGE technology may support data rates of up to 384 Kbps. The EDGE technology may utilizes 8 phase shift keying (8-PSK) modulation for providing higher data rates than those that may be achieved by GPRS technology. The GPRS and EDGE technologies may be referred to as “2.5G” technologies.
The Universal Mobile Telecommunications System (UMTS) technology with theoretical data rates as high as 2 Mbps, is an adaptation of the WCDMA 3G system by GSM. One reason for the high data rates that may be achieved by UMTS technology stems from the 5 MHz WCDMA channel bandwidths versus the 200 KHz GSM channel bandwidths. The High Speed Downlink Packet Access (HSDPA) technology is an Internet protocol (IP) based service, oriented for data communications, which adapts WCDMA to support data transfer rates on the order of 10 megabits per second (Mbits/s). Developed by the 3G Partnership Project (3GPP) group, the HSDPA technology achieves higher data rates through a plurality of methods.
Where HSDPA is a downlink protocol, High Speed Uplink Packet Access (HSUPA) technology addresses the uplink communication. HSUPA is also specified by the 3GPP group to provide a complement data link to HSDPA. HSUPA also offers broadband IP and is based on software. HSUPA also extends the WCDMA bit rates, but the uplink rates may be less than the downlink rates of HSDPA. Where prior protocols severely limited the uplink connections, HSUPA allows for much higher uplink rates.
Likewise, standards for Digital Terrestrial Television Broadcasting (DTTB) provide for transmission of broadcast video. Three leading DTTB systems are the Advanced Television Systems Committee (ATSC) system, the Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) system, and the Digital Video Broadcasting (DVB) system, which includes terrestrial transmission under Digital Video Broadcasting-Terrestrial (DVB-T) specifications and transmissions to handheld devices under Digital Video Broadcasting-Handheld (DVB-H) specifications. DVB-H is an adaptation of DVB-T to handheld units, in which additional features are implemented to meet specific requirements of handheld units. DVB-H allows downlink channels with high data rates and may be made as enhancements to current mobile wireless networks. DVB-H may use time slicing technology to reduce power consumption of handheld devices.
In order to practice the various protocols, a wireless communication device is utilized. For a wireless communication device to participate in wireless communications, it typically includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). The transmitter typically includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with a local oscillator signal to produce radio frequency (RF) signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
The receiver is coupled to an antenna and typically includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The one or more intermediate frequency stages mix the amplified RF signals with a local oscillator signal to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
Generally, when a wireless device, such as a mobile 3G transceiver, is in a transmit mode of operation, the device operates under a particular communication standard and/or protocol. The communication standard specifies specific frequency bands and power levels that a particular device is allowed to transmit. The specific transmission requirements are set by the communication standard based on the designated band, public or commercial use of the frequency, type of transmission, as well as other criteria. The frequency bands and transmission requirements may also vary depending on the geographic location, whether it be a region, country or continent.
The various communication standards also typically require strict adherence to requirements that prevent out-of-band transmissions from the transmitter in order not to interfere with other bands, channels and/or frequencies. The 3G standards also have restrictions placed on spurious emissions outside of the designated permitted transmission band. One of the causes of spurious emissions in a RF front end of a transmitter is due to the operation of the mixer in mixing the baseband or IF signal with a local oscillator signal to generate the RF signal. Although various suppression techniques or filtering may be used to reduce the spurious emissions, one component that contributes to such spurious emissions remains fixed. That component is the harmonics generated by the reference frequency (which is also defined as the comparison frequency) of the reference signal input to the transmitter local oscillator.
In a typical local oscillator (LO) that generates a LO signal used by the transmitter, a reference frequency source, such as a crystal source, sets the reference frequency (or comparison frequency; noted as Fcomp) signal for input to the LO, which may employ a phase-locked loop (PLL) circuitry for generating the local oscillator signal. The harmonics of the comparison frequency (noted as N*Fcomp, where N is an integer) combine with the transmit signal FTX to produce harmonic induced spurious emissions Fharm at the output. For example, equation Fharm=FTX±N*Fcomp exemplifies a harmonic signal generation that results in a spurious emission at the output of the transmitter. In some instances, this type of spurious emission may not violate restrictions specified by a particular communication standard, but in other instances, the spurious emissions may result in out-of-band transmission that is in violation of a standard.
Unfortunately, when Fcomp is fixed, the harmonic generation due to Fcomp is also pre-determined and those harmonic frequencies are also fixed. Therefore, when such harmonic generation has a potential for out-of-band transmission which are restricted by a communication standard, the transmitter may need to implement some form of suppression technique for suppressing such harmonic transmission. However, if transmitters can be designed with selectable Fcomp signals that take into consideration the various out-of-band restrictions based on a plurality of communications standards (or protocols) in use, then harmonic generation from the Fcomp signal would not contribute to unwanted out-of-band spurious emissions from a transmitter.
Therefore, a need exists for a technique to implement an agile frequency planning scheme for generating the Fcomp signal as a reference input to the transmitter LO, in which the frequency planning scheme considers restrictions placed on spurious emissions dictated by one or more communication standards or protocols.